Radio receiver



July 13, 1937. R. M. SMITH RADIO "RECEIVER Filed May :51 1955 2Sheets-Sheet 1 vusnn'ron "SHIELD P0 wan Jilin w. 39 37 5a LII I h a v M.p w ,2 T. F mwq v 3 LIA Iv 1 VII il 9; .3 .Al k7 T 4 l 1,

HT'T'ORNEY July 13, .1937. R. M. SMITH RADIO RECEIVER Filed May 51, 19352 Sheets-Sheet 2 A re Mfl/IV RECEIVER C 1/1955/5 Wes-s6.-

INVEN'T'OR Rogers M.5'miih MW H'T'TORNE'Y' Patented July 13, 1937 UNlTEDSTATES PAT FHQE

RADEO RECEIVER tion of Delaware Application May 31, 1935, Serial No. 21L233 '7 Claims.

The present invention relates to radio receivers, and more particularlyto radio receivers for motor vehicles and the like which must operate inthe presence of ignition and power supply short wave interference.

It is, therefore, an object of the present invention to provide a radioreceiver wherein the effects of ignition and similar interference arematerially reduced or prevented.

It is a further object of the present invention to provide an improvedtuner arrangement for the high frequency portion of a radio receivingsystem whereby interference from circulating electrical current in thechassis is prevented from entering the high frequency circuits.

It is also a further and specific object of the present invention toprovide a shielded radio receiver construction including a variabletuning high frequency selector means as a unit which is immune fromelectrical currents circulating in the chassis and from vibrationalforces tending to disturb the tuning adjustment in a manner to produceacoustic feed back.

While the normal operating or generating frequency of the usual sourceof energy such as an ignition system or a'vibratory radio power supplydevice, causing radio interference may be relatively low, connectionleads and devices providing oscillatory circuits connected therewith maycause interference at very high frequencies. For example, a six cylindercar with the engine rotating at 2000 revolutions per minute may produceapproximately sparks per second. This 100 cycle frequency gives noappreciable direct disturbance in shielded radio apparatus. However,each high tension lead has inductance and capacity to the car body whichmakes it part of an oscillatory circuit. This oscillatory circuitradiates energy for each spark, The fundamental frequency depends uponthe length of the ignition wires and their placement in relation toadjacent metallic objects. High tension currents from a coil radiatehigh frequency energy which is induced into the low tension light wires,the metallic car body and other metallic parts which are in closerelationship to it.

For high frequency currents, the wave length may be only a few feetwhich may cause standing waves to appear in the car body. High frequencyvoltages may, therefore, be large at some points on the body andnegligible at other points. At extremely high frequencies the voltagesare very high and the highest interference area is found between 2 and.11 meters.

Energy radiated by wires and circulating cur- (Cl. 250 m) rents inconducting material such as the casing of a receiver may enter thereceiver through the antenna and lead in or through the control cables,power supply leads and other external connections in which voltages maybe induced. 5 Energy may also enter the receiver through openings in thereceiver casing such as ventilating openings. Furthermore, energy mayenter the receiver through circulating currents which are set up in thecasing itself and, since the casing is normally grounded, particularlyin a vehicle type of receiver, external leads through the casing providea path for such circulating currents. Heretofore the entry of energyinto a receiver through circulating currents and through openings hasbeen disregarded as unimportant and apparently it has not been realizedthe extent to which such interference may become large in proportion tointerference through other channels above mentioned. 20

It is, therefore, a still further object of this invention to provide aradio receiver having an outer casing with the inner elements thereofarranged and assembled to avoid the effects of circulating currents inthe casing and to prevent noise voltages from being induced into thesensitive section of the receiver. At the same time, it is also providedthat tuning system which is sensitive to vibration, may be protectedtherefrom.

It is also a further object of the present invention to provide a tuningmeans in a radio receiver which is substantially mechanically andelectrically isolated both from circulating currents throughout thechassis and from vibration of the chassis.

It is a still further object of the invention to provide a receiverconstruction adapted for use in connection with a vibratory or otherinterference producing source of power therefore without introducinginterference energy into the sensitive receiving circuits thereof fromsaid source,

The invention will, however, be better understood from the followingdescription when considered in connection with the accompanying drawingsand its scope will be pointed out in the appended claims.

In the drawings, Figure 1 is a view partly in section, of a portion of aradio receiver embodying the invention;

Figs. 2, 3, 4 and 5 are current flow diagrams illustrating the paths ofvarious circulating currents and waves in a radio receiver when subjectto interference energy, Figs. 3 and 5 illustrating diagrammatically, theisolation afforded by the construction shown in Fig. 1, of the sensitiveportions of the receiver from such interference; and

Fig. 6 is a schematic wiring diagram of a tuning system in a radioreceiver also embodying the invention.

Referring to Fig. 1, 5 represents one side wall of a radio receivercasing having closed top and bottom members I and 9 respectively, allcomposed of conducting material such as steel, for example, in which ismounted, in spaced relation to the walls, high frequency receivingapparatus comprising a gang variable tuning condenser I I and associatedtuning inductances represented by the inductance I3, connected therewithby leads I5, and having individual metallic shield casings indicated atIT.

The tuning condenser I I and the tuning inductances I3 are mounted onand electrically grounded to a separate base plate or sub-base I9 whichis also spaced from the casing and from the receiver chassis or mainbase 3|, by suitable spacing and supporting members providing flexibleor resilient mechanical connection with the casing or chassis.

In the present example, such means comprises rubber washers 23interposed between the sub-base I9 and the main chassis 2|, throughwhich a suitable clamping screw 25 engages the base for clamping thesub-base I9 to the chassis 2I. An enlarged opening 2'! in the chassisbase is provided about the screw 25 so that the connection between thesub-base I9 and the chassis is insulated electrically. The connectionbetween them is mechanical only with a large degree of flexibilityafforded by the material of the washers, which is preferably softrubber.

In the present example, the sub-base or plate I9 is bent at an angle asshown to permit the mounting of the condenser II and the inductances I3in a Vertical plane adjacent to the side wall 5 of the casing, and forthat reason an ad ditional spacing or buffer member of. resilientmaterial, such as rubber, is provided as indicated at 29, to engage thewall 5 thereby to space the plate I9 from the wall adjacent to the upperfree end 3|.

The condenser I I is of the usual metallic shielded type, and circuitwiring is made directly from the condenser to the coils or inductancesrepresented at I3, so that the high frequency tuning elements and theirassociated circuits are included on the mounting plate or sub-base I9,which in turn, is mechanically connected by resilient means to thechassis or casing, but not electrically. The tuning unit is, therefore,isolated from the remainder of the apparatus both electrically againstcirculating currents and mechanically against vibration tending to causeacoustic feedback through vibration of the condenser plates.

A single flexible electrical connection 33 is made to the radio chassisby a single wire or braid soldered or otherwise secured to the mountingplate I9 as indicated at 20 and connected to the radio chassispreferably at a single point of low potential with respect tocirculating currents. The connection may be provided by a bolt 22 whichis preferably provided with a terminal as indicated at 35 to whichconnection is made from the common ground point to other apparatusdirectly by wire 3'! as indicated by the tube base terminal 39. The tubeis indicated in the drawings as being enclosed in a shield 47. The gridconnection for the tube is provided through a lead II to the condenserII. Other ungrounded circuit connections are made to the apparatus onthe sub-base or mounting plate I9 as indicated by the lead 43.

Thus a one point ground is provided for the high frequency or tunedcircuit portion of the receiver, thereby preventing undesirablecirculating chassis currents from passing through any portion of. thesensitive portions of the receiver. The spacing of the internal elementsfro-m the casing and the individual shielding of the elements furtherprevent inductive pickup from such currents.

A main source of energy and of vibration which may be included in thereceiver casing, is represented by a vibrator power unit 49. As is wellknown, devices of this character include current interrupter means whichmay cause radio interference similar to that produced by the ignitionsystem of the vehicle with which the receiver is usually associated. Itwill be seen that in Fig. 1, the radio frequency amplifier or highfrequency portion of the receiver and, in particular, the tuned circuitsare completely isolated as a unit electrically and mechanically from thevibrator power unit, so that disturbing currents may not flow from thelatter in coupling relation to the elements of the tuning unit.

It will also be noted that a screen 42 of suitable woven metal Wire isprovided over an opening 44 representing any openings such as those forventilation. This represents the treatment employed for all chassis andcasing openings of any size to prevent coupling with the tuning unit bywaves or electrostatic energy.

In Figs. 2, 3, 4, and 5 the outline chassis and receiver diagramsindicate the flow of chassis currents from an interference source ofenergy such as a vibrator power unit, or from an ignition source ofinterference and serve to illustrate how interference therefrom isprevented in a high frequency tuning unit when mounted as shown in Fig.1.

Referring now to Fig. 2, a receiver, represented by the rectangularenclosure R, contains, among other things, a power supply unit P and atuning unit C, the enclosing lines representing metallic walls providinga shield around each of the units named. The power unit P is known to bea source of interference, the generating element therein being indicatedat G, which causes circulating currents I to flow as indicated by thearrows in the metallic members of the power unit as well as in thereceiver chassis and the container for the tuning unit C. At ultra highfrequencies the chassis members may approach a wave length in length orwidth. Therefore, it is possible to produce standing waves indicated atW or portions thereof in the receiver casing, for example.

Since the power unit is mounted on the receiver chassis, as indicated inFig. 2, and is provided with input and output connections such as A andB, it is known to induce currents I the receiver parts, chassis andcasing as indicated by the arrows. Ihe radio frequency or tuning unit Cbeing the most sensitive portion of the receiver is most susceptible tothese interfering currents and common practice has led to the connectionarrangement shown, wherein the receiver tuning element is connected tothe chassis or casing for the receiver at more than one point formechanical or electrical reasons, as represented at D and E, forexample. This causes a certain portion of the interference current to bepassed through the unit C as indicated by the arrows and results in whatis commonly called static or interference.

Referring now to Fig. 3, it will be seen that the unit C is isolatedfrom the casing R and connected therewith by a single connection D whichis in accordance with the showing in Fig. 1. Since a complete circuitdoes not exist through the unit C, circulating currents I will notchoose this path in their return circuit, thereby eliminatinginterference in the high frequency portion of the receiver.

Fig. 3, therefore, represents diagrammatically the arrangement ofapparatus as shown in Fig. 1 wherein the parts P and C are spaced apartfrom each other and from the casing and'in which the part C iselectrically isolated from the remainder of the apparatus for theconduction of circulating currents.

Referring now to Fig. 4, the source of interference G and the powersupply unit P, together with the high frequency tuning unit C,'are thesame as in Figs. 2 and 3 but with an additional source of interferenceG1 which may represent an ignition system carried by the chassis of anautomobile, indicated diagrammatically at T. The receiver R is assumedto be mounted on the frame or chassis T by connections M, N, O and Qproviding electrical and mechanical connections therewith for thereceiver. 1

The ignition system may produce interference currents I1 as indicated bythe arrows, or standing waves W1, in addition tothe currents and wavesresulting from the interference source G as described in connection withFigs. 2 and 3 and omitted in the present figure for the sake ofclearness. It will be seen that the current flow from the source G1 issuch that with connections, as shown, the interference currents willcouple with the high frequency tuning portion C of the receiver therebygiving additional interference.

However, it will be seen that in case the high frequency tuning unit Cis isolated electrically and mechanically and provided with a singleconnection D to the chassis or frame of the receiver as in Fig. 5,-theexternal source of interference may not have coupling therewith, wherebythe interference from that source is prevented.

The electrical circuits of a suitable tuning unit including the electricdischarge amplifier devices which may be incorporated in a unit such asshown in Fig. l and diagrammatically indicated at C in the succeedingfigures, a unit of this type is shown in Fig. 6 to which attention isnow directed. This is a schematic circuit diagram of the radio frequencytuning portion of a superhetero-dyne receiver, for example, in which atube 5| of the pentode type is utilized as a radio frequency amplifierand a second tube 53 is utilized as a combined detector and oscillator.

In the present example, a three unit tuning condenser is indicated bysections 55, 5'! and 59, arranged to have a common grounded rotorconnected as shown, to a sub-base or mounting plate indicated at 6|. Themounting plate is electrically isolated from the main receiver chassisrepresented at 53 by resilient mounting means 6 preferably of rubber,and is provided with a single flexible connection 65 to the mainchassis.

All of the electrical circuits of the tuning unit normally connecteddirectly with a receiver main chassis are connected, instead, to thesub-base or plate 5! as shown. Such circuits include the input circuit51 for the radio frequency amplifier 5! comprising the portion 55 of thetuning condenser and the secondary of the input or antenna couplingtransformer 69, the tuned'input circuit H for the combined detectoroscillator 53 comprising the section 51 of the tuning condenser and thesecondary of the coupling transformer 13, and the oscillator tunedcircuit which includes the section 59 of the tuning condenser and theoscillator coupling coil H. It will be noted that all of said circuitsare suitably by-passed to the plate or sub-base 5| through suitableby-pass condensers represented at 19.

The high frequency tuning unit and the sensitive receiving circuitsthereof are, therefore, connected to the sub-base 6| which is providedwith a single connection to the main chassis for the supply of operatingpotentials, thereby prevented the flow of circulating currents throughthe tuner as a unit.

It has been found that this arrangement has materially aided in theprevention of noise in receivers for radio reception in the home and inparticular in the automobile type of receiver which is subjected to bothtypes of interference represented in the drawings, particularly in Figs.4 and 5.

This chassis and circuit arrangement represents a portion of a generalsystem for the prevention or elimination of interference from externaland internal sources associated with a radio receiver and serves adefinite purpose effectively and by means which may be applied in anyreceiver construction at low cost.

I claim as my invention:

1. A radio receiver comprising in combination, a metallic casing, ametallic base member mounted therein, radio receiving apparatus mountedthereon including a power supply unit, a high frequency tuning unitincluding a separate base plate mounted on said base member in spacedelectrically insulated relation thereto and to the casing walls, saidtuning unit further comprising a plurality of high frequency receivingcircuits connected to said base plate and including tuning inductancesand capacities, and means providing a single electrical connectionbetween said base plate and said base member whereby said tuning unit isgrounded thereto by a single electrical connection to preventcirculating currents flowing in said base member from being included insaid base plate and tuning unit.

2. In a radio receiver, the combination of a chassis unit comprising abase member and an outer Casing, a high frequency tuning unit sensitiveto circulating currents in the base member and comprising a tuningdevice and a tuning inductance, a separate base and ground member forsaid device and inductance, means for resiliently mounting said secondnamed base member in spaced electrically insulated relation to the firstnamed, member and casing, and means providing a single electrical groundconnection from the high frequency tuning unit to the first named basemember, whereby undesirable circulating currents in said base member areprevented from flowing in the high frequency unit and from coupling withthe apparatus thereon and connected therewith.

3. In an automobile radio receiver having a power supply unit whichoperates to set up undesirable circulating currents, and a metallicchassis on which said power unit is mounted and in which said currentstend to flow, of means including a metallic base member for separatelymounting the sensitive elements of said receiver including highfrequency tuning circuits. insulating means for resiliently supportingsaid base member in spaced relation to the chassis, means providing asingle flexible electrical connection between said base member and thechassis at a predetermined point on said chassis, and means forgrounding each of said circuits to said base member thereby to completesaid circuits within the tuning unit to the exclusion of the receiverchassis and the circulating currents therein.

4. A radio receiving system including a plurality of tunable circuitsand electric discharge amplifier devices connected therewith foramplifying and transforming signals received in said circuits, ametallic member providing a common supporting and grounding means forelectrical elements included in said circuits and a common groundconnection for said circuits, means for resiliently mounting saidmetallic member in insulated spaced relation to the remainder of saidreceiver, and means providing a single grounding connection thereto withthe remainder of said receiver to prevent circulating currents flowingin the remainder of said receiver from being included in said metalliccommon supporting and grounding member and the circuits connectedtherewith.

5. A radio receiver comprising a metallic casing providing a shieldedcontainer, means providing a plurality of tuned high frequency receivingcircuits therein and including a tuning condenser and a tuninginductance, means for electrically shielding said condenser andinductance, means providing a metallic base member for said condenserand inductance to which the shielding means are grounded by directconnection, a receiver chassis, resilient rubber mounting means forelectrically and mechanically separating said base member and associatedapparatus from the receiver chassis, power supply means carried by saidchassis and connected therewith whereby circulating currents are causedto flow therefrom through the chassis, and means providing a singleelectrical connection between said base member and said chassis at apredetermined point to prevent the flow of said currents in saidmetallic base member.

6. A radio receiving system including a plurality of tunable circuitsand electric discharge amplifier devices connected therewith foramplifying and transforming signals received in said circuits, ametallic member providing a common supporting and grounding means forelectrical elements included in said circuits and a common groundconnection for said circuits, means for mounting said metallic member ininsulated spaced relation to the remainder of said receiver, and meansproviding a single grounding connection thereto with the remainder ofsaid re ceiver to prevent circulating currents flowing in the remainderof said receiver from being included in said metallic common supportingand grounding member and the circuits connected therewith.

'7. A radio receiving system including a plurality of tunable circuitsand electric discharge amplifier devices connected therewith foramplifying and transforming signals received in said circuits, ametallic member providing a common supporting and grounding means forelectrical elements included in said circuits and a common groundconnection for said circuits, means for mounting said metallic member ininsulated spaced relation to the remainder of said receiver, and meansproviding effectively a single grounding connection thereto with theremainder of said receiver to prevent circulating currents flowing inthe remainder of said receiver from being included in said metalliccommon supporting and grounding member and the circuits connectedtherewith.

ROGERS M. SMITH.

